Mud weighing unit

ABSTRACT

A new and improved device for determining the density of flowing drilling mud which includes a pneumatic level transmitter mounted on a vessel through which the drilling mud flows. The pneumatic level transmitter senses the buoyant force exerted on a displacer element immersed in the drilling fluid flowing through the vessel; and a special flow directing means is mounted in the housing at the inlet in order to control and direct the flow of drilling mud into a substantially circular pattern to eliminate substantially all forces except buoyancy which might otherwise act on the displacer element by the flowing drilling mud.

United States Patent [191 Bell [ Jan. 1,1974

[ MUD WElGl-lING UNIT 211 Appl. No.: 178,714

Primary Examiner-Richard C. Queisser Assistant Examiner-Stephen A. Kreitman AttorneyPravel, Wilson & Matthews [57] ABSTRACT A new and improved device for determining the density of flowing drilling mud which includes a pneumatic level transmitter mounted on a vessel through which the drilling mud flows. The pneumatic level transmitter senses the buoyant force exerted on a displacer element immersed in the drilling fluid flowing through the vessel; and a special flow directing means is mounted in the housing at the inlet in order to control and direct the flow of drilling mud into a substantially circular pattern to eliminate substantially all forces except buoyancy which might otherwise act on the displacer element by the flowing drilling mud.

5 Claims, 4 Drawing Figures MUD WEIGHING UNIT BACKGROUND OF THE INVENTION 1. Field of the Invention The field of this invention is measurement of the buoyant force exerted by a flowing fluid such as drilling mud in order to determine the density of the drilling mud, or the level of the drilling mud in a vessel.

2. Description of the Prior Art In oil well drilling operations, it is customary to circulate a drilling fluid or mud, usually down through the drill string, about the drill bit and then up the annulus between the wall of the drilled hole and the drill string. During such drilling operations, an unexpected increase in downhole pressure, commonly called a kick, is controlled by temporarily increasing the density of the drilling mud to counteract the downhole pressure increase. As the kick subsides and the downhole pressure gradually decreases to normal, the density of the drilling mud is also gradually decreased. Therefore, in performing such operation, it is important that the actual density of the drilling mud be continually monitored so that it can be adjusted as necessary.

To determine the density or level in a vessel of a fluid, such as drilling mud, a device such as the pneumatic buoyancy level transmitters of the Foxboro Company, of Foxboro, Massachusetts, is used to measure the buoyant force exerted by the fluid since changes in the buoyant force indicate changes in the density of liquid level. These level transmitters which will be de scribed in greater detail later, include a displacer element that is partially or totally immersed in the fluid being measured and is pivotally suspended from a transmitter that provides an output signal responsive to vertical movement of the displacer element.

When the Foxboro pneumatic transmitter or a similar device is used to measure the density of a flowing fluid, the displacer element is completely immersed in the flowing fluid. One difficulty in measuring a flowing fluid is that the displacer element may be moved laterally in an unpredictable manner due to the motion of the flowing fluid. Such extraneous lateral movement is undesirable since it is likely to cause the pivotally suspended displacer element to be moved vertically which will adversely affect the accuracy of the sensing of buoyant force. Also, the lateral movement of the displacer element may cause the rather delicate transmitter members connected to the displacer element to bind, thus preventing free vertical movement in response to the buoyant force exerted by the fluid.

One attempt to solve the problem of accurately measuring a flowing fluid was to install a stilling well or a cage around the displacer element to try to eliminate the flowing motion of the fluid thereabout. Guide rings have also been installed about the displacer element to prevent lateral movement of the element. However, stilling wells andcages are undesirable since they prevent free circulation of the fluid about the displacer element thereby increasing the likelihood of particles precipitating out of the quiescent fluid, which may eventually result in deposits such as well cuttings that interfere with the operation of the level transmitter. The rings are also not generally satisfactory since the forces exerted by the flowing fluid may cause the displacer element to chafe against the rings.

SUMMARY OF THE INVENTION A measuring means is mounted in a cylindrical vessel with a displacer or buoyant element immersed in the fluid, which may be drilling mud, flowing through the vessel. To prevent the motion of the flowing fluid from affecting the accuracy of the measuring means, a special flow directing means is mounted about the vessel inlet to direct the fluid into a substantially circular flow pattern about the displacer element which minimizes lateral forces acting on the measuring means while still getting an accurate buoyancy effect from the drilling fluid, and without the disadvantages of the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the buoyant force measuring device according to the preferred embodiment of this invention;

FIG. 2 is a sectional view of the buoyant force measuring device of the present invention taken along line 2-2 of FIG. 1;

FIG. 3 is a sectional view of the transmitting apparatus used in the invention; and

FIG. 3A is a detailed view of the control relay used in the transmitting apparatus shown in FIG. 3.

With reference to FIG. 1 of the drawing, a device A is illustrated for measuring the buoyant force exerted by a flowing fluid, such as drilling mud, to determine the density of the fluid. The measuring device A includes a cylindrical vessel B on which a measuring means C is mounted.

The vessel B includes an upper cylindrical section 10a and a lower conical section 10b connected thereto. An inlet 11 in cylindrical housing section 10a allows a fluid such as drilling mud to enter and circulate through the cylindrical section 10a down into the lower conical housing section 1012 and out through a bottom outlet 13.

An overflow outlet 14 is mounted on the cylindrical section 10a of the vessel B. A pump P is provided for pumping fluid, such as drilling mud, through incoming line 11a, which is mounted on the vessel B at the inlet 11. The incoming line 11a includes a tee llb that diverts flow through line 110, which leads to a fluid reservoir (not shown) such as a mudpit if the fluid is drilling mud. A valve 11d is mounted in line 11c. to control the amount of fluid diverted into vessel B; and a valve 13b is mounted in bottom outlet line 13a to cooperate with valve lid in controlling the rate of fluid flow through the vessel B and the level 10f fluid in the vessel B.

The measuring means C is, for example, a pneumatic level transmitter Model 17B which is sold by the Foxboro Company. Such a pneumatic level transmitter is itself conventional and well known and it generally includes a transmitter unit 15 which is mounted on a pipe 10c extending from a top wall 10d of the vessel B by means of an elbow joint 16. A housing 18 for the transmitter unit 15 includes a cover 18a, and a collar assembly 18b mounted on the cover 18a to provide an aperture 180. The elbow joint 16 is threadedly connected to the cover and the collar assembly 18b by means of bolts 16a and 16b. A diaphragm seal 20 is mounted in the aperture 18c so that the inside of the cover 18a is protected against the entry of fluids from the vessel B. A force bar 17 extends through the diaphragm seal.

A displacer element 21 is suspended from end 17a of the force bar 17 by means of a connecting rod 22 which is attached to the displacer element, and a twisted metal strip 23, which connects the rod 22 to end 17a of the force bar. ln the embodiment shown in FIG. 3, the metal strip 23 has an aperture (not shown) so that the strip fits over the end 17a of the force bar and a bolt 24 is screwed into the end 17a to hold the strip 23 thereon. The lower end of the strip 23 may have a hole or eye 23a for receiving a hook 22a on the upper end of the rod 22 to facilitate removal of the displacer 21 for cleaning purposes.

The displacer element 21 is totally immersed in the fluid flowing through the vessel B, and moves vertically upwardly and downwarldy in response to changes in the density of the fluid circulated through the vessel. The transmitter unit is designed to provide a pneumatic output signal through an output line 30 which is proportional to the amount of vertical movement of the displacer element 21 in response to the buoyant force exerted on the displacer element by the fluid. Since there is a direct mathematical relationship between the buoyant force exerted by the fluid and the density of the fluid, the transmitter unit may be used to indicate the density of the fluid flowing through the vessel simply by attaching the output line 30 to a properly calibrated gauge.

For the transmitter unit 15 to provide an output signal through the output line 30 indicative of the buoyant force or density of the fluid, the unit must be extremely sensitive to the slightest vertical movement of the displacer element 21. The transmitter 15 has a supply air pressure line 31 which connects to a control relay 32 and a by-pass line 33. The by-pass line 33 includes a reducingtube 34 which reduces the volume of flow of the supply air to a pressure sensing line 35, which is connected to the control relay 32 at one end and has a nozzle 36 connected at its open end whereby a continuous flow of air, at a reduced volume, is vented to atmosphere through the nozzle 36. A feedback line 37 is connected to the control relay 32 and to a feedback bellows 38, which is suspended from a transmitter housing support 18d. The output line 30 is connected to the feedback line 37 and extends to a gauge (not shown) which indicates the change in density of the fluid due to a change in output pressure in line 30.

The force bar 17, which is pivotal about the diaphragm seal 20, has attached at end 17b a flexure connector 39. The flexure connector 39 is also attached to a range rod 40 which pivots about a range wheel 41, which is threadably engaged on the range rod 40 and pivots on a support arm l8e of the transmitter housing. Thus, whenever the displacer element 21 is moved vertically, the force bar 17 is pivoted about the diaphragm seal so that the flexure connector 39 causes the range rod 40 to pivot about the range wheel 41.

Attached at one end of the range wheel 40 is a flapper 42 and at the other end is an arm 43 which connects to the feedback bellows 38. A set screw 44 threadedly extends through the housing support 18d to adjust the compression in a spring 45 which urges the arm 43 mounted on the range wheel 40 downwardly and the flapper 42 upwardly away from the nozzle 36.

The control relay 32 furnishes an air pressure signal through the feedback line 37 to the output line 30 and to the feedback bellows 38 and responds to changes in the air pressure in pressure sensing line 35. The control relay 32 includes a housing 49 which is rectangular in the cross-sectional view shown in FIGS. 3 and 3A and has a center wall 49a having an aperture 50 disposed therein. The center wall 49a basically divides the relay housing 49 into an upper chamber 49b and a lower chamber 490. The supply air line 31 is connected into the upper chamber 49b and the pressure sensing line 35 is connected into the lower chamber 490. The lower chamber 490 includes an opening 51 to atmosphere. The feedback line 37 is in communication with both the upper and lower chambers within the control relay.

A diaphragm 52 is connected across the lower chamber 49c to enclose a portion thereof below the opening 50 so that the pressure in pressure sensing line 35 acts upon the diaphragm. A conical exhaust valve 53 is mounted onto the upper surface of the diaphragm 52 and a valve stem 54 extends upwardly from the conical exhaust valve and has a supply ball valve 55 mounted on its upper end, the supply ball valve 55 being positioned in the upper chamber 49b.

Generally, the incoming supply pressure through line 31 is at approximately 20-25 p.s.i., while the output signal through line 30 is designed to vary from 3 to 15 psi. in a linear relationship to the amount of displacement of the displacer element 21 due to the buoyant force exerted thereon by the fluid flowing through the vessel B.

The actual pressure of the output signal through line 30 is dependent upon the position of the diaphragm 52 which controls the seating and unseating of the supply ball valve 55 and the conical exhaust valve 53. When diaphragm 52 moves downward, in response to a loss in pressure in pressure sensing line 35 and in the enclosed portion of lower chamber 490, the supply ball valve is moved downwardly toward a seated position in the aperture 50 against the center wall 49a and the feedback line 37 so that the supply of air to feedback line 37 is cut off. Thus,as the pressure in pressure sensing line 35 decreases, the output pressure through output line 30 decreases. When the diaphragm is in the position shown in FIG. 3, then neither the supply ball valve 55 nor the conical exhaust valve 53 is seated in aperture 51. Therefore, the supply air from line 31 flows both into feedback line 37 and through the aperture 50 and out through the opening 51 in the lower chamber 49c. When the diaphragm 52 is moved upwardly due to an increase in pressure in pressure sensing line 35 and the enclosed portion of the lower chamber 49c, the conical exhaust valve 53 is moved towards a seated position against the lower edges of the aperture 50 thereby increasing the air supply into feedback line 37 and thus the pressure in the output line 30.

Thus, the control relay is basically a continuously bleed type, with some air flow passing through the aperture 50 almost continuously unless either the supply ball valve 55 or the conical exhaust valve 53 are seated in the aperture 50. For the purpose of describing the operation of the measuring means C, let us assume the diaphragm is in the position shown in FIG. 3, which would mean that density being measured is at a value near the median in its expected range.

When the density of the fluid flowing through the vessel decreases, from this assumed median value, the displacer element 21, being heavier than the fluid per unit weight, will be moved vertically downward since the buoyant force exerted on the displacer element will decrease. As the displacer element is moved downwardly, the force bar 17 pivots about the diaphragm seal 20 so that the end 1712 of the first force bar is moved upwardly. As the end 17b of the force bar moves upwardly, the upward movement of the attached flexure connector causes the range rod 40 to pivot about the range wheel 41.

As the range rod 40 pivots in a clockwise direction about the range wheel, the flapper 42 is moved upwardly and the arm 43 is moved downwardly. The downward movement of the arm 43 causes the feedback bellows 38 attached to the arm to also be moved downwardly thereby increasing the volume within the feedback bellows resulting in an immediate reduction in pressure within the bellows and feedback line 37. At the same time, the flapper 42 is moved upwardly away from the nozzle 36 thereby causing a decrease in pressure at the nozzle and thus a decrease in pressure within pressure sensing line and the enclosed portion of lower chamber 490. The decrease in pressure within the enclosed portion of the chamber 490 will cause the diaphragm 52 to move downwardly and the supply ball valve 55 to seat, or almost seat,(depending upon the amount of the pressure drop) in the aperture 50. The seating of the ball valve 55 in the aperture 50 blocks off, either fully or partially, depending upon the degree of seating of the ball valve 55 in the aperture, the supply of air from supply line 31 into feedback line 37. This, of course, causes a decrease in pressure in line 37. Therefore, the pressure in the output line 30 is decreased since both the supply air pressure coming into line 37 through the control valve and the pressure in the feedback bellows 38 is decreased.

The control valve 32 is an extremely sensitive unit; therefore, the diaphragm will oscillate slightly until a steady-state relationship is reached between the pressure in the feedback bellows 38 and the position of the diaphragm 52. The steady-state position is attained for the decrease in density when the moments, taken about range wheel 41, of the. upward forces exerted by the flexure connector 39 and the pressure of the venting air at nozzle 36' acting on the flapper 42, equals the moments acting downwardly, the downward acting forces being the forces exerted by the pressure in the feedback bellows 38 and the spring 45.

lf the density of the fluid flowing through the vessel increases thereby causing the displacer 21 to move up wardly, end 17b of the force bar 17 is caused to move downwardly. The downward movement of end 17b of the force bar causes the range rod 40 to pivot counterclockwise so that the flapper 42 is moved downwardly toward the nozzle 36 and the arm 43 is moved upwardly'. The downward movement of the flapper 42 closer to the nozzle 36 causes an increase in pressure at that point and in pressure sensing line 35 while the upward movement of the arm 43 also cause a contraction of the feedback bellows 38.

The increase in pressure in pressure sensing line 35 causes an increase in pressure in the enclosed portion of the lower chamber 49c in the control relay thereby moving upwardly the diaphragm 52 which causes the conical exhaust valve 53 to seat fully or partially against the lower part of the aperture 50. The seating of the conical exhaust valve causes the amount of air flowing into feedback line 37 to increase thereby increasing the pressure in the output line 30. At the same time, the contraction of the feedback bellows 38 under the upward movement of the arm 43 causes an increase in pressure in the bellows and in line 30. In this manner, the output pressure in output line 30 increases as the density of the fluid flowing through the vessel B increases.

The preferred buoyancy level transmitter is thus an extremely sensitive unit and therefore will provide an output signal at line 30 in response to any vertical movement of the displacer 21. Hence, it is extremely important that essentially the only force acting on the displacer 21 be the buoyant force of the fluid. The unpredictable nature of any extraneous forces produced by the motion of flowing fluid cannot be adjusted for in the buoyancy level transmitter itself. Of course, it is understood that these extraneous forces caused by the motion of the fluid may be actually lateral rather than vertical in direction; but the lateral forces will cause a swinging of the displacer 21 which produces vertical movement.

To eliminate these extraneous forces, a flow control means, generally designated as 60, is mounted on an inside wall 10c of the vessel 10 to direct the flow of fluid in a substantially circular flow pattern about the displacer element 21 to assist in assuring that essentially only the buoyant force of the fluid is exerted on the displacer element. The flow control means is disposed over the inlet 11 and is spaced radially inwardly therefrom, and is closed at one lateral end 60a and open at the other lateral end 60b so that fluid entering the vessel through the inlet 11 is directed through the open end 60b.

The flow control means 60 is preferably a plate 61 having a substantially vertically disposed planar section 61a which is connected to the inner wall l0e of the vessel at one lateral end 60a. The plate 61 further includes a top section 62 and a bottom section 63 attached to the inner vessel wall 102 and to the vertical section 16a and wherein each of the sections 62 and 63 has curved outer surface conforming to the curvature of the inner wall We and attached thereto. In this manner an opening 64 is formed at the other end 60b of the plate between the vertical plate 61a and the inside vessel wall 10c.

' The angle at which a pipe 63 enters through inlet 11 is such that the fluid entering engages the vertical section 61 at an oblique angle such that the velocity component along the tangential direction of arrow 66 is less than the velocity of the fluid at the inlet 11. Further, the cross-sectional area of the opening 64 is substantially larger than that of the inlet, which also contributes to a decrease in the velocity of the fluid from the inlet 11 to the opening 64.

The flow control means 60 is mounted below the level 10f of the fluid in the vessel and above the vessel outlet 13. The position of the flow directing means, in combination with the angle at which the entering fluid engages the plate, prevents the formation of a harmful amount of turbulent flow, which might otherwise exert extraneous lateral forces on the displacer element. By employing such a flow control means, the fluid flowing about the displacer element 21 exerts no resultant lateral force on the displacer so that essentially only the buoyant force exerted by the fluid acts thereon. The fluid discharges through the outlet 14 at the lower end of the vessel B which is disposed below the inlet 11. Thus, the fluid flowing through the housing may carry with it and discharge through the outlet 14, any particles or debris which might be with the fluid rather than collect same in the vessel B. It is to be noted that, even if there is turbulence in the vicinity of the displacer ball 21, it is not sufficient to cause false readings of the fluid density.

Substantially all vertical flow forces by the fluid in the vessel B are substantially eliminated by providing for the fluid flow upwardly and downwardly from the inlet 11 to the upper overflow outlet 14 and the bottom outlet 13. These upward and downward vertical forces substantially cancel each other to further minimize turbulence and reaction on the displacer element 21 when the flow rate through the overflow outlet 14 is approximately equal to the flow rate through the bottom outlet 13. In the preferred embodiment of the invention, the valves 11d and 13b are adjusted manually or otherwise so that the flow rate through overflow outlet 14 is substantially equal to the flow rate through bottom outlet 13. To prevent putting an undue load on the pump P when regulating the inlet flow through line 11a to the vessel B, the valve lld diverts a portion of the fluid from the pump through the line 11c back to the mud pits or pump for recirculation. In this manner, the pressure which the pump is working against is as low as possible and the pump will be allowed to put out its full volume at all times.

The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials as well as in the details of the illustrated construction may be made without departing from the spirit of the invention. For example, the displacer element 21 may be in the form of a closed cylinder rather than being spherical as illustrated.

I claim:

1. A device for measuring the buoyant force of a flowing fluid, such as drilling mud, comprising:

a. a substantially cylindrical vessel through which said fluid flows and including an inlet at which said fluid enters the vessel;

b. mud density measuring means suspended in said vessel for vertical movement in response to changes in the buoyant force of said flowing fluid, said measuring means including a displacer element disposed in said fluid flowing through said vessel whereby said measuring means provides an output signal indicative of the buoyant force exerted by said displacer element and thereby the density of the fluid; and

c. flow control means with said vessel including a plate disposed over said inlet and spaced inwardly therefrom and secured to said vessel at one lateral end to close said one end and spaced from said vessel at the other lateral end to provide an open end whereby fluid entering said vessel is directed through said open end for substantially preventing turbulent flow of said fluid about said displacer element whereby essentially only the buoyant force of said fluid is exerted on said displacer element.

2. The device set forth in claim 1, wherein said flow control means includes means for discharging said flowing fluid substantially tangentially into said vessel to create said substantially circular flow pattern.

3. The device set forth in claim 1 wherein:

said flow control means includes a plate has a substantially vertically disposed section attached to said vessel at one lateral end, and top and bottom sections attached to said vessel and to said vertical section.

4. The device set forth in claim 1, wherein:

said inlet is positioned such that entering fluid engages said plate at an oblique angle for substantially reducing the fluid velocity and turbulence prior to the discharge of the fluid into said vessel.

5. The device set forth in claim 1, wherein:

said open end of said flow control means is substantially larger in cross-sectional area than said inlet whereby the velocity of said fluid entering said vessel from said plate is decreased as compared to the 

1. A device for measuring the buoyant force of a flowing fluid, such as drilling mud, comprising: a. a Substantially cylindrical vessel through which said fluid flows and including an inlet at which said fluid enters the vessel; b. mud density measuring means suspended in said vessel for vertical movements in response to changes in the buoyant force of said flowing fluid, said measuring means including a displacer element disposed in said fluid flowing through said vessel whereby said measuring means provides an output signal indicative of the buoyant force exerted by said displacer element and thereby the density of the fluid; and c. flow control means with said vessel including a plate disposed over said inlet and spaced inwardly therefrom and secured to said vessel at one lateral end to close said one end and spaced from said vessel at the other lateral end to provide an open end whereby fluid entering said vessel is directed through said open end for substantially preventing turbulent flow of said fluid about said displacer element whereby essentially only the buoyant force of said fluid is exerted on said displacer element.
 2. The device set forth in claim 1, wherein said flow control means includes means for discharging said flowing fluid substantially tangentially into said vessel to create said substantially circular flow pattern.
 3. The device set forth in claim 1 wherein: said flow control means includes a plate has a substantially vertically disposed section attached to said vessel at one lateral end, and top and bottom sections attached to said vessel and to said vertical section.
 4. The device set forth in claim 1, wherein: said inlet is positioned such that entering fluid engages said plate at an oblique angle for substantially reducing the fluid velocity and turbulence prior to the discharge of the fluid into said vessel.
 5. The device set forth in claim 1, wherein: said open end of said flow control means is substantially larger in cross-sectional area than said inlet whereby the velocity of said fluid entering said vessel from said plate is decreased as compared to the fluid velocity at said inlet. 